The recognition of mother squirrel monkeys by their infants by means of odor has been examined by exposing infants to their own and other mothers who have been anesthetized. Tests with additional sensory exposure to both anesthetized and awake real mothers also have been conducted to determine to what degree different sensory modalities contribute to the infant's recognition and attachment. The results of these experiments have shown that infant squirrel monkeys can recognize their mothers solely on the basis of odors, and that additional sensory information tends to facilitate such behavior. Moreover, physical contact with the mother selected on the basis of odor is effective in reducing distress. In other studies the significance of early olfactory experience on behaviroal development is being examined with infants raised with mothers (either natural or surrogate) that have been treated with artificial odors.